Nippon Telegraph and Telephone Corporation

Fujitsu Corporation

Gentaro Funatsu

Hideki Maeda

Shinichirou Harasawa

Akira Naka

Hiroyuki Deguchi

Masahito Tomizawa

Akira Hirano

Kazushige Yonenaga

Akihide Sano

Shoichiro Kuwahara

Tomoyoshi Kataoka

Mikio Yoneyama

Takayuki Maehara

An optical transmission system is provided in which the optimum operating point of a Mach-Zehnder interferometer, matched to the optical frequency of the light source on the transmitting side, can be set. The optical receiver () has an infinitesimal-modulated signal component detection circuit (), which uses the signal train output from a balanced detection circuit () to detect the infinitesimal-modulated signal component applied to the phase adjustment terminal () of an MZI () by an infinitesimal-modulated signal oscillation circuit (); a synchronous detection circuit (), which synchronously detects the infinitesimal-modulated signals output from the infinitesimal-modulated signal component detection circuit () and infinitesimal-modulated signal oscillation circuit () and detects the error signal component arising from the shift between the optical signal carrier frequency and the optical frequency characteristic of the MZI (); and a controller (), which outputs a control signal to adjust the phase difference between two split optical signals output from the MZI () so as to correct the shift amount.

Optical transmission system, optical transmitter for optical transmission system, and optical receiver for optical transmission system

The present invention provides an automatic power restoring method capable of reliably detecting continuity by the dissolution of a line fault, to restore the optical power, even in a structure including an optical amplification medium on an optical transmission path and an optical communication system using the method. To this end, in an optical communication system to which the automatic power restoring method of the invention is applied, a pilot signal having a low transmission rate, a wavelength of which is set based on loss wavelength characteristics obtained by combining loss wavelength characteristics of an optical fiber used for the optical transmission path and loss wavelength characteristics of the optical amplification medium on the optical transmission path, is transmitted and received between an optical transmitting station and an optical receiving station when a line fault occurs, and a detection of continuity is thus performed. According to the result of the continuity detection, the power state at the occurrence of line fault is automatically restored to the power state at a time of normal operation.

Automatic power restoring method and optical communication system

In a method for performing OTDR measurement in an optical transmission system including a first terminal station and a second terminal station, OTDR signal light is transmitted from an OTDR provided in the first terminal station to the second terminal station, in which the OTDR signal light is Raman amplified by using main signal light of the optical transmission system as pump light.

Measurement method by OTDR and terminal station apparatus

Growing community of inventors

Yokohama, Japan

Gentaro Funatsu